6 Detailed Description

6.1 Overview

The TL331-Q1 is a single comparator with the ability to operate up to 36V on the supply pin. This standard

device has proven ubiquity and versatility across a wide range of applications. This is due to the very wide

supply voltage range (2V to 36V), low Iq, and fast response.

The open-collector output allows the user to configure the output's logic low voltage (VOL) and can be utilized to

enable the comparator to be used in AND functionality.

The TL331B-Q1 and TL391B-Q1 are performance upgrades to industry standard TL331-Q1 using the latest

semiconductor process technologies that allows for lower offset voltages, lower input bias and supply currents

and faster response times. The TL331B can drop-in replace the "I" or "Q" versions of TL331-Q1. The TL391B-

Q1 is an alternate pinout of the TL331B-Q1 for replacing competitive devices.

6.2 Functional Block Diagram

- Input

Q2

Q1

Q3

Q4

Q9

Q10

Q11

Q5

Q6

D1

D2

D3

D4

Q7

Q8

Q12

+ Input

Output

VCC

Internal

Bias

Itail

I1

I2

Q13

Q14

ESD

ESD

VCM

Clamp

Q15

6.3 Feature Description

The TL331-Q1 consists of a PNP Darlington pair input, allowing the device to operate with very high gain and

fast response with minimal input bias current. The input Darlington pair creates a limit on the input common

mode voltage capability, allowing TL331-Q1 to accurately function from ground to VCC – 1.5V differential input. A

clamp (Q15) was added around Q3 to force the output low when both inputs are taken above the VCM range.

The output consists of an open collector NPN (pull-down or low side) transistor. The output NPN sinks current

when the negative input voltage is higher than the positive input voltage and the offset voltage. The VOL is

resistive and scales with the output current. Please see Output Low Voltage vs. Output Sinking Current at 5V for

VOL values with respect to the output current.

6.4 Device Functional Modes

6.4.1 Voltage Comparison

The TL331-Q1 operates solely as a voltage comparator, comparing the differential voltage between the positive

and negative pins and outputting a logic low or high impedance (logic high with pull-up) based on the input

differential polarity.

TL331-Q1, TL331B-Q1, TL391B-Q1

SLVS969H – OCTOBER 2009 – REVISED JANUARY 2025

www.ti.com

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